L5: Solar System Models and Formation

Multiple Choice

Why did early astronomers believe that the Earth was stationary?

• They believed the Earth was stationary because celestial bodies appeared to move around it.
• They assumed the Sun revolved around the Earth due to its brightness.
• They believed the stars were fixed in place.
• They thought the Earth was flat and couldn't move.

Models of the Solar System

Early astronomers saw the sun, stars, and moon moving across the sky each day and thought everything in space moved in a circle around Earth. The belief that Earth is the center of the universe is called a geocentric theory. Although the geocentric model explained the motion of the sun, moon, and stars, it failed to explain many other observations. For example, planets have phases like the moon, and the geocentric model could not easily explain or predict them. Planets were also seen moving backward in the sky from night to night, which is why word “planet” comes from the Greek word for “wanderer.” However, the geocentric model could not easily explain this odd motion of the planets either.

Multiple Choice

Define geocentric.

• Geocentric means Sun-centered.
• Geocentric means Earth-centered.
• Geocentric refers to a model of the universe with stars at the center.
• Geocentric is a term used for oceanic studies.

Models of the Solar System

Scientific models must be able to predict new events and fit with all known evidence. Although the geocentric model had many flaws, it was widely accepted for over 1,500 years. It was not until the 1540s during the Scientific Revolution that Nicholas Copernicus developed an improved model in which Earth and other planets orbit the sun. This idea is called a heliocentric theory and also known as the Copernican theory. The heliocentric model fit better with all the evidence and could more easily explain the backward (retrograde) motion of the planets. 

Multiple Choice

Define orbit.

• An orbit is a fixed position in space.
• An orbit is the speed at which an object travels through space.
• An orbit is the gravitational pull exerted by a planet.
• The path an object takes as it moves around another object.

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Models of the Solar System

A century later, Galileo would use the heliocentric model to also explain and predict the phases of Venus. The heliocentric model changed our ideas of astronomy forever. Other scientists continued to build on Copernicus’s ideas over the next centuries. Our modern picture of the universe is the result of all their work. 

Multiple Choice

What questions exposed weaknesses of the geocentric model of the solar system?

• Questions about the size of the Earth
• Questions about retrograde motion, varying brightness of planets, and stellar parallax.
• Questions regarding the speed of light
• Questions about the composition of the Sun

Multiple Choice

Why did the heliocentric theory become widely accepted?

• It was based on ancient myths and legends.
• The theory was proposed by a single scientist without evidence.
• It was widely accepted due to political pressure from the church.
• The theory became accepted due to strong evidence and mathematical support from key astronomers.

Formation of the Solar System

Scientists believe the solar system formed about 5 billion years ago from a huge swirling cloud of gas and dust particles in space. Gravity caused the particles to clump together as the cloud rotated. Eventually, the center of the cloud became so dense and massive that its gravity caused everything around it to collapse inward and form a star. This star is our sun, and its mass makes up 99.8 percent of the solar system. The remaining dust, rocks, and particles around the sun continued to clump together due to gravity to form the planets. This process by which particles collect under the force of gravity to form larger bodies is called accretion.

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Multiple Choice

How did Jupiter form?

• Jupiter formed from the solar nebula through accretion of gas and dust.
• Jupiter was created by the gravitational pull of Saturn.
• Jupiter was formed by a collision of asteroids.
• Jupiter originated from the remnants of a supernova explosion.

Multiple Choice

Why did it become a gas giant?

• It became a gas giant because it was formed from solid materials.
• It became a gas giant due to its small size and density.
• It became a gas giant as a result of a collision with another planet.
• It became a gas giant due to its ability to attract and retain large amounts of gas.

Formation of the Solar System

The effects of accretion can still be observed today as larger bodies continue to attract (or accrete) bits of matter from across the solar system. Space rocks are constantly hitting the planets and moons every day. Scientists estimate that Earth attracts over two tons of space dust every hour. On occasion, gravity can even bring a large asteroid or comet on a collision course with a planet. Jupiter, our solar system’s largest planet, continues to be hit by a large object every 5 to 30 years. Surface craters on moons and terrestrial planets provide additional evidence of how accretion causes objects in space to increase in mass.

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Multiple Choice

Why are meteors attracted to Earth and other planets?

• Meteors are attracted to Earth due to magnetic fields.
• Meteors are attracted to Earth and other planets because of their gravitational pull.
• Meteors are drawn to Earth because of solar winds.
• Meteors are pulled towards Earth by atmospheric pressure.

Formation of the Solar System

The fact that the planets move in the same plane around the sun is another piece of evidence for the theory of how the solar system formed. If you trace the motion of the planets, their paths appear to form a flat disk. This is because when the cloud that formed the solar system collapsed, it began rotating faster. The rapid spinning motion caused the matter around it to flatten into a disk with the sun at the center. As the material in this swirling disk clumped together and accreted, they formed larger bodies that became the planets. This explains why all the planets move in nearly the same plane around the sun.

Formation of the Solar System

Today, the planets continue to orbit in the same direction that the original cloud was spinning. All planets revolve in a counterclockwise direction, when viewed from above Earth’s North Pole. They also all rotate or spin counterclockwise, except for Venus. Scientists do not know exactly why Venus rotates in the opposite direction. A long-held theory is that it was struck billions of years ago by a planet-sized object that had enough mass to flip the entire planet’s rotation around.

Match

Match the following

• mass

• accretion

• revolve

the quantity of matter in a body

particles come together due to gravity

to move in a circular or elliptical path

• the quantity of matter in a body

• particles come together due to gravity

• to move in a circular or elliptical path

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Multiple Choice

Why did the rocky planets form closer to the sun?

• Rocky planets formed due to gravitational pull from larger planets.
• Rocky planets are made of ice and formed far from the sun.
• Rocky planets formed from gas clouds that cooled down.
• Rocky planets formed closer due to higher temperatures allowing only metal and rock to condense.

Multiple Choice

How did the sun and planets form?

• The sun and planets formed from solid rocks colliding in the universe.
• The sun and planets formed from a solar nebula through gravitational collapse and accretion.
• The sun and planets were created by a giant explosion in space.
• The sun and planets originated from ancient stars that burned out completely.

Word Cloud

What caused the craters of the moon?

Multiple Choice

What was the effect of gravity on the formation of the solar system, and how does it explain motion in the solar system today?

• Gravity only affects the Earth and not other celestial bodies.
• The solar system formed without any influence from gravity.
• Gravity has no effect on the solar system's formation.
• Gravity caused the collapse of the solar nebula, leading to the formation of the Sun and planets.

Categorize

Options (7)

The sun orbits Earth.

The sun appears to move across the sky.

The moon appears to move across the sky.

The planets appear to move across the sky

Earth and other planets orbit the sun.

The moon orbits Earth.

Planets orbit Earth.

Decide whether each statement applies to a geocentric model, heliocentric model, or both.

geocentric

heliocentric

both

Multiple Choice

Which of the following statements describes the formation of the solar system? 

• Gravity caused a nebular cloud to swirl and form the planets before the sun.

• The planets created a cloud of gas and dust that collapsed to form the sun.

• A vast cloud of gas and dust collapsed and gave rise to planets.

• Gravity among dust and gas particles formed the sun and planets.